Azo coupling of 2-nitroanilines with 2,4,-disbustituted phenols

Abstract

A process for the preparation of compounds of the formula I is described ##STR1## in which R 1 and R 2 independently of one another are C 1 -C 7 alkyl; and R 3 is hydrogen or halogen, by reaction of a diazonium salt of a 2-nitroaniline in acid aqueous solution with a phenol dispersed in water. The process comprises employing as the dispersant a C 8 -C 20 alkanesulfonic acid or a corresponding alkanesulfonate or a mixture of sulfonic acid and sulfonate together with a polyvinyl alcohol. The resulting compounds of the formula I can advantageously be reacted further to give benzotriazoles of the formula V ##STR2## which are used as light stabilizers.

What is claimed is: 
     
       1. A process for the preparation of a compound of the formula I ##STR16## in which R 1  and R 2  independently of one another are C 1  -C 7  alkyl; and R 3  is hydrogen or halogen, by reaction of a diazonium salt of a 2-nitroaniline of the formula II ##STR17## in acid aqueous solution with a phenol of the formula III ##STR18## dispersed in water, in which the radicals R 1  to R 3  are as defined in formula I, which comprises employing as the dispersant a C 8  -C 20  alkanesulfonic acid and/or a corresponding alkanesulfonate together with a polyvinyl alcohol. 
     
     
       2. A process according to claim 1, in which R 1  and R 2  independently of one another are C 1  -C 5  alkyl; and R 3  is hydrogen or chlorine. 
     
     
       3. A process according to claim 2, in which R 1  and R 2  independently of one another are methyl or branched C 3  -C 5  alkyl. 
     
     
       4. A process according to claim 1, wherein an alkanesulfonic acid and/or the sodium or potassium salt thereof together with a polyvinyl alcohol of molecular weight 10,000 to 250,000 are employed as the dispersant. 
     
     
       5. A process according to claim 1, wherein the alkanesulfonic acid or alkanesulfonate is employed in an amount of 0.5 m 10% by weight and the polyvinyl alcohol is employed in an amount of 0.1 to 5% by weight, in each case based on the theoretical amount of azo compound of the formula I. 
     
     
       6. A process according to claim 5, wherein the dispersant comprises 1 to 20 parts by weight of polyvinyl alcohol per 10 parts by weight of alkanesulfonic acid and/or alkanesulfonate. 
     
     
       7. A process according to claim 1, wherein the alkanesulfonic acid or alkanesulfonate is derived from a straight-chain alkane. 
     
     
       8. A process according to claim 1, wherein the temperature is kept in the range of 20° to 60° C. throughout the entire coupling reaction. 
     
     
       9. A process according to claim 1, wherein the phenol of the formula III is employed in a 1 to 5% molar excess over the 2-nitroaniline of the formula II. 
     
     
       10. A process for the preparation of a compound of the formula V ##STR19## in which R 1  and R 2  independently of one another are C 1  -C 7  alkyl; and R 3  is hydrogen or halogen, by a) reaction of a diazonium salt of a 2-nitroaniline of the formula II ##STR20## in acid aqueous solution with a phenol of the formula III ##STR21## dispersed in water, to form the intermediate product of the formula I ##STR22## and b) subsequent reduction of the intermediate product of the formula I to form the compound of the formula V,   which comprises employing as the dispersant in step (a) a C 8  -C 20  alkanesulfonic acid or a corresponding alkanesulfonate or a mixture of sulfonic acid and sulfonate together with a polyvinyl alcohol.